Generally, moment of inertia isn't scalar $I$ but tensor $\tilde{I}$. The exact equation is
$$\vec{L} = \tilde{I} \vec{\omega}$$
which means that generally vectors $\vec{I}$ and $\vec{\omega}$ do not have the same direction! The expression you wrote
$$\vec{L} = I \vec{\omega}$$
where $I$ is simply a scalar is that it is valid only if the body rotates only around one of the three principal axes of moment of inertia.
For all other rotations things become increasingly complex and you have to use Euler's equations. Angular momentum $\vec{L}$ is of course always conserved if there are no external moments, and $\vec{L}$ is therefore constant, but taking Euler's equations angular velocity $\vec{\omega}$ generally is not constant!
Since football is highly symmetric body, it is easy to identify its principal axes of moment of inertia and it is obvious that $I_{xx} = I_{yy} > I_{zz}$.